1. Field of the Invention
The present invention relates to a method of recording a digital video signal.
2. Description of the Prior Art
A variety of video signals are now available for use with not only the existing NTSC (60 Hz), PA-L (50 Hz), and SECAM (50 Hz) systems but also advanced High Definition television (HDTV) systems (50/60 Hz) including the MUSE system (60 Hz) of a frequency bandwidth compression type and the HD-MAC system (50 Hz). In particular, a video signal in digital form is more preferred and for recording such a digital video signal, a digital VTR (video tape recorder) has been developed. For example, a known digital VTR for use in broadcasting service employs the D-1 method for recording two different TV signals in one common format (See SMPTE 224M: "Proposed American National standard for component digital video recording 19-mm type D-1 cassette-tape record").
The D-1 method is designed for recording of video signals of two different TV systems; one, like NTSC, provides 525 lines for one frame scanned at a rate of about 30 frames per second (referred to as a 525-line system hereinafter) and the other, like PAL or SECAM, provides 625 lines for one frame scanned at about 25 frames per second (ref erred to as a 625-line system hereinafter) one frame consists of two fields and in the D-1 method, data is recorded in each field. Hence, the number of fields per second is about 60 in the 525-line system and about 50 in the 625-line system. Also, the total of effective pixels per field for a luminance component of the video signal is expressed as 720 columns by 250 rows in the 525-line system and 720 columns by 300 rows in the 625-line system. As understood, both the 525-line and 625-line systems are almost equal in the number of effective pixels for each second (fields x horizontal pixels x vertical pixels). In the D-1 method, the effective pixels for one field are grouped into 10.times.300 segments of the 525-line system and 12.times.300 segments of the 625-line system so that each segment can contain an equal number of pixels. 300 of the segments are then recorded onto each track of a recording tape.
Two major disadvantages of the above D-1 method will now be explained.
(1) Although the effective pixels of the 525-line system are aligned in 250 lines, actual image data of the video signal occupy 242 lines. Also, 288 lines of the 625-line system, other than 300 lines, are filled with actual image data of the video signal. The D-1 method provides a surplus of effective pixels in the vertical direction for the purpose of setting the number of segments per track to 300. As the result, more than a desired data has to be recorded and the consumption of a recording tape will be increased. If such a redundant data is recorded onto a cassette tape, the cassette tape of considerable size is needed. However, a smaller size of the cassette tape is preferred for use with a home VTR than that of a broadcasting system VTR using the D-1 method.
(2) The D-1 method provides the foregoing format for recording two different video signals of the existing TV systems and fails to work with any HDTV system which will soon be in service.